A PCp would ideally be much smaller, lighter, and easier to handle than a laptop. The performance, cost, and purpose of a PCp are dissimilar to those of a laptop.
Ultra-portable laptops focus on business work, gaming laptops are by no means portable, and all laptops consume a large amount of space (Volume = length x width x width) when open.
PCp's give you a sense of achievement that laptops usually don't. For instance, why build a NESp when 20 bazillion devices can emulate NES consoles with reasonable performance and compatability, and the ability to perform many other tasks?